Fact Sheet: Announcement of
Completion of EPA's Third Six-Year
Review of Existing Drinking Water
Standards
United States
Environmental Protection
Agency
The Safe Drinking Water Act (SDWA) requires EPA to review each National Primary Drinking Water
Regulation (NPDWR) at least once every six years and revise them, if appropriate. The purpose of the
review, called the Six-Year Review, is to identify those NPDWRs for which current health effects
assessments, changes in technology, and/or other factors provide a health or technical basis to support a
regulatory revision that will maintain or strengthen public health protection.
Questions and Answers
1.	What is the Environmental Protection Agency (EPA) announcing?
In December 2016, the Agency announced the completion of its third review of existing NPDWRs
(i.e., the Six-Year Review 3). Based on the Agency's detailed review of 76 NPDWRs, the Agency
determined that 68 of them remain appropriate (i.e., do not need to be revised) and that eight NPDWRs
are candidates for regulatory revision. These eight NPDWRs are included in the Stage 1 and the Stage
2 Disinfectants and Disinfection Byproducts Rules, the Surface Water Treatment Rule, the Interim
Enhanced Surface Water Treatment Rule and the Long Term 1 Enhanced Surface Water Treatment
Rule. The eight NPDWRs are chlorite, Cryptosporidium, Giardia lamblia, haloacetic acids (HAA5),
heterotrophic bacteria, Legionella, total trihalomethanes (TTHM) and viruses. In addition to 76
NPDWRs, this review includes 12 other NPDWRs that did not need a detailed review because of
recent, ongoing, or pending regulatory actions.
2.	Why did EPA conduct a review of the National Primary Drinking Water Regulations (NPDWRs)?
The 1996 Safe Drinking Water Act (SDWA) Amendments require EPA to conduct a review of existing
NPDWRs every six years and determine which, if any, need to be revised. This requirement is contained in
Section 1412(b)(9) of SDWA, which reads:
The Administrator shall, not less often than every 6 years, review and revise, as appropriate, each national
primary drinking water regulation promulgated under this title. Any revision of a national primary
drinking water regulation shall be promulgated in accordance with this section, except that each revision
shall maintain, or provide for greater, protection of the health ofpersons.
3.	What NPDWRs are covered by this action?
The Six-Year Review process only applies to NPDWRs (i.e., currently regulated
contaminants/parameters). Unregulated contaminants, such as those listed on the Contaminant Candidate
List (CCL), are not covered by the Six-Year Review. The current review specifically focused on the 76
regulations promulgated prior to August 2008. The Agency included 12 other NPDWRs (e.g., lead, copper,
trichloroethylene (TCE) and tetrachloroethylene (PCE)) in the review. However, these regulations did not
need a detailed assessment because they are the subject of recent, ongoing, or pending rulemaking activity.
4. How did EPA review the NPDWRs under Six-Year Review 3?
A detailed description of the process the Agency used to review the NPDWRs is documented in the "EPA
Protocol for the Third Review of Existing National Primary Drinking Water Regulations." The foundation
of this protocol was developed for the Six-Year Review 1 based on the recommendations of the National
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Drinking Water Advisory Council. The Six-Year Review 3 process is very similar to the process
implemented during the Six-Year Review 1 and the Six-Year Review 2, with some clarifications to the
elements related to the review of NPDWRs included in the Microbial and Disinfection Byproducts Rules.
The protocol for the Six-Year Review 3 is broken down into a series of questions that can inform a
decision about the appropriateness of revising an NPDWR. These questions are structured into a decision
tree related to the following review elements considered for each NPDWR during the Six-Year Review 3:
initial review, health effects, analytical feasibility, occurrence and exposure, treatment feasibility, risk
balancing and other regulatory revisions.
Figure 1. Six-Year Review Protocol Overview and Review Outcomes
Yes
No
No
•Uncertain - emerging
No
Yes
No
* Contaminants with an HEA in process that have an MCL based on practical
quantitation limit and are greaterthan MCLG are passed to the next question to
evaluate potential to revise the MCL.
NPDWR reviewed in recent or ongoing action?
NPDWRs Under Review
assessment (HEA)
in process or planned? *
Data sufficient to support
regulatory revision?
New information to suggest possible changes (i.e...
to an MCLG, MCL, Treatment Technique and/or
other regulatory revisions)?
Meaningful opportunity for health risk reduction for
persons served by PWSs and-'or cost savings while
maintaining'improving public health protection?
5. What are the overall review results for Six-Year Review 3?
Based on its review, EPA finds that eight NPDWRs are candidates for regulatory revision. These eight
NPDWRs are chlorite, Cryptosporidium, Giardia lamblia, HAA5, heterotrophic bacteria, Legionella, TTHM,
and Viruses. EPA believes the remaining 68 NPDWRs are not appropriate for revision due to one or more of
the following reasons:
•	Regulatory action - recently completed, ongoing or pending. The NPDWR was recently
completed, is being reviewed in an ongoing action, or is subject to a pending action.
•	Ongoing or planned health effects assessment. The NPDWR has an ongoing health effects
assessment (i.e., especially for those NPDWRs with an MCL set at the MCLG or where the MCL
is based on the SDWA cost benefit provision), or EPA is considering whether a new health effects
assessment is needed.
•	No new information. EPA did not identify any new, relevant information that indicates changes to
the NPDWR.
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• Low priority and/or no meaningful opportunity. New information indicates a possible change to
the MCLG and/or MCL but changes to the NPDWR are not warranted due to one or more of the
following reasons: (1) possible changes present negligible gains in public health protection; (2)
possible changes present limited opportunity for cost savings while maintaining the same or
greater level of health protection; and (3) possible changes are a low priority because of
competing workload priorities, limited return on the administrative costs associated with
rulemaking and the burden on states and the regulated community associated with implementing
any regulatory change that would result.
Table 1 lists the results of EPA's review for each of the 76 NPDWRs that received a detailed review, along
with the principal rationale for the review outcomes. Table 1 also includes a list of the 12 NPDWRs that were
recently completed, are being reviewed in an ongoing action, or are subject to a pending action.
6.	Will EPA consider reviewing any NPDWRs before the next review cycle?
If the result of an ongoing health risk assessment or the resolution of data gaps/research needs indicates that
significant or compelling new information becomes available that will change the basis for an NPDWR, the
Agency may decide to accelerate the review schedule for a particular NPDWR.
7.	What are the next steps?
The Agency requests public comment on the eight NPDWRs identified as candidates for revision, as well as
other relevant comments. EPA will consider comments received as the Agency moves forward with
determining whether regulatory actions are necessary for the eight NPDWRs.
8.	Where can I find more information about this notice and the Six-Year Review?
For information on the Six-Year Review, please visit the EPA internet website,
https://www.epa.gov/dwsixyearreview.
For general information on drinking water, please visit the EPA Office of Ground Water and DrinkingWater
website at https://www.epa.gov/ground-water-and-drinking-water or contact the Safe Drinking Water
Hotline at 1-800-426-4791. The Safe Drinking Water Hotline is open Monday through Friday, excluding
legal holidays, from 10:00 a.m. to 4:00 p.m. Eastern Time.
Table 1. Summary of Six-Year Review 3 Results
Not
Appropriate
for Revision
at this Time
Recently
completed,
ongoing or
pending
regulatory action
1,2-Dichloroethane
(Ethylene dichloride)
E. coli
1,2-Dichloropropane
Lead
Benzene
Tetrachloroethylene (PCE)
Carbon Tetrachloride
Total coliforms
(under ADWR and RTCR)
Copper
Trichloroethylene (TCE)
Dichloromethane
(Methylene chloride)
Vinyl chloride
Not
Appropriate
for Revision
at this Time2
Health effects
assessment in
process (as of
December 2015)
or contaminant
Alpha/photon emitters
Mercury1
Arsenic
Nitrate1
Atrazine
Nitrite1
Benzo(a)pyrene (PAHs)
o-Dichlorobenzene1
Beta/photon emitters
p-Dichlorobenzene1
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nominated for
health
Cadmium1
Polychlorinated biphenyls
(PCBs)

assessment
Chromium
Radium


Di(2-ethylhexyl) phthalate
(DEHP)1
Simazine


Ethylbenzene
Uranium1


Glyphosate



1,2-Dibromo-3 -chloropropane
(DBCP)
Dalapon

No new
information,
NPDWR
2,4,5 -TP (Silvex)
Di(2-ethylhexyl)adipate
(DEHA)

Antimony
Dinoseb

Asbestos
Endrin

remains
Bromate
Ethylene dibromide

appropriate after
Chloramines (under D/DBPR)
Pentachlorophenol

review
Chlorine (under D/DBPR)
Thallium


Chlorine dioxide
trans-1,2-Dichloroethylene


Chlorobenzene
(monochlorobenzene)
Turbidity


1,1,1 -Trichloroethane
Epichlorohydrin


1,1,2-Trichloroethane
Fluoride


1,1 -Dichloroethylene
Heptachlor


1,2,4-Trichlorobenzene
Heptachlor epoxide


2,3,7,8-TCDD (Dioxin)
Hexachlorobenzene


2,4-D
Hexachlorocyclopentadiene

Low priority
and/or no
Acrylamide
Lindane

Alachlor
Methoxychlor

meaningful
Barium
Oxamyl (Vydate)

opportunity
Beryllium
Picloram


Carbofuran
Selenium


Chlordane
Styrene


cis-l,2-Dichloroethylene
Toluene


Cyanide
Toxaphene


Diquat
Xylenes


Endothall



Chlorite
Heterotrophic Bacteria
Candidate for
Revision
New
information
Cryptosporidium
(under SWTR, IESWTR, LT1)
Legionella

Giardia lamblia
TTHM


Haloacetic Acids (HAA5)
Viruses (under SWTR)
1.	Contaminants nominated for Integrated Risk Information System (IRIS) assessments per SYR Protocol.
2.	LT2, FBRR, and GWR also identified as not appropriate for revision at this time. See Section VI.B.4
for additional information on the results of EPA's review of these regulations.
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